GitLab has been updated to version 18. Information about changes can be found at: https://about.gitlab.com/blog/2025/04/18/a-guide-to-the-breaking-changes-in-gitlab-18-0/#breaking-changes
This aligns the condition in ov_vendortree.h with the condition in ov_vendortree.c.
Fixes build with OV_VALGRIND flag. Fixes #1 (closed)